In live broadcast productions, several separate input channels may be input to a single broadcast location or to several broadcast locations linked together, for example, by satellite or microwave. The several inputs are processed and mixed together at a studio facility. In order to facilitate such a broadcast production from the various signals, it is necessary to provide a monitor signal of the mixed output signal to each of the input locations so that the persons providing the inputs may interact with each other. However, when the mixed signal is provided to a remote location it may result in feedback or an echo effect from a delayed return.
For example, a talk show based in Los Angeles, Calif. may include a host in Los Angeles conducting an interview with a person in a studio in London, England. The talk show audio and video signals would be sent as a monitor feed to the location in London, and might include audio signals from the interviewer as well as from the audience. Likewise, the interviewer and the audience would require a monitor feed to hear the interviewee. Most likely, the audio monitor feed from London would be sent to Los Angles via satellite, travelling a large distance in between. Due to this distance, a delay is introduced into the monitor signal. When received and routed through a mixing console in Los Angeles, the incoming signal would be placed in the broadcast signal path and the monitor signal path. If this monitor signal is rebroadcast to London, an additional delay is introduced. The result would be an "echo" of the interviewee's voice when received back in London.
FIG. 1 depicts such a situation. A signal starting with the interviewer's microphone at the main studio 2 passes through an audio mixer from where it is sent via a satellite 6 to a remote studio or mobile location 4 via transmitting equipment. This signal is received at the remote location with a slight time delay t=d/r where d is the distance travelled and r is the signal speed.
The interviewee's audio signal travels back along this same path from the remote location 4 to the main studio 2 with the same delay t. However, the signal from the remote location 4 would be mixed with the audio from the main studio 2 and distributed back to the remote location over the same path. As a result, the interviewee would hear his voice with an echo of 2 t.
In order to avoid this problem, the monitor signal sent back to the remote location 4 could have the audio signal from the remote location removed. For example, the remote signal could simply be not assigned to the monitor path. However, as the number of feeds increases, it becomes difficult to keep track of each signal that is to be assigned. This increases the risk that a monitor signal will lack all the signals intended to be monitored, or will contain a signal originating from the monitor location thereby causing feedback or echo effects.
There is accordingly a need to provide an audio mixing system in which each location may be provided with a monitor feed which lacks an input signal originating from the monitor location. There is a further need to accomplish this goal in a manner which is not prohibitively expensive and which is relatively convenient.